PROJECT SUMMARY/ABSTRACT The impact of disease beliefs on self-management of chronic illness such as diabetes (DM) in the setting of cancer is largely unknown. In addition, little is known about the impact of age- or cancer-related cognitive changes on cancer survivors? self-management behaviors (SMB) for their other comorbidities. Without this knowledge, our ability to provide optimal self-management support for cancer survivors with comorbidities is limited. The goal of this study is to determine how disease beliefs about cancer and DM and cognitive changes affect older breast cancer survivors? DM SMB. We will focus on older breast cancer survivors with early-stage cancer who have received chemotherapy or hormonal therapy (HT) since these patients are more likely to have age- or cancer-related cognitive changes and are more likely to die from complications from their comorbidities as from their breast cancer. We will focus on DM due to its high prevalence in cancer survivors, association with worse cancer outcomes and cognitive decline, impact on competing risks of death, and its moderate SMB complexity. The study design is rooted in the Common Sense Self-Regulation Model (CSM), a theory of health behaviors that has been used to develop interventions, but has primarily been applied to research on behaviors around single diseases. By understanding the relationship between disease beliefs about breast cancer and DM and the interrelationship of disease beliefs and cognitive function on survivors? DM SMB, we will advance both the CSM and care of older breast cancer survivors with comorbidities. The Specific Aims are to: 1) Evaluate the longitudinal interrelationship of beliefs about breast cancer and DM and its effect on survivors? DM SMB (adherence to medications, diet and exercise); 2) Assess the effect of cognitive function on DM SMB and evaluate whether disease beliefs mediate, in part, an association between cognition and DM SMB; and 3) Develop and pilot an educational and counseling intervention to improve DM SMB among breast cancer survivors with comorbid DM. This prospective cohort study will recruit 320 older (?55 years) breast cancer survivors with pre-existing DM who have completed first-line chemotherapy or are taking hormonal therapy for treatment of early stage (I-IIIA) breast cancer within the past 5 years. We will first conduct qualitative interviews with 20 survivors to identify DM and cancer health beliefs and to elicit specific strategies and routines used to manage DM. We will then recruit 300 participants and interview them every 6 months for 24 months to assess longitudinal changes in cancer and DM beliefs and in cognition to evaluate their impact on DM SMB. For the subgroup of women currently taking HT, we will also assess the impact of beliefs and cognitive function on HT adherence. We will integrate the information collected in the quantitative and qualitative interviews to create educational and counseling modules and pilot test their impact on SMB on a group of 100 breast cancer survivors with DM. The proposed study addresses the need to develop strategies to optimize SMB for chronic comorbidities in cancer survivors using breast cancer and DM as the paradigm.